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Chernobyl: Countdown to Meltdown

On April 26, 1986, a nuclear nightmare turned into reality after an explosion and fire in reactor four at the Chernobyl nuclear plant in Ukraine, near the border of Belarus. The disaster, caused by a combination of human error and design flaws at the plant, would become the worst nuclear accident in human history.

This satellite photo provides a 2009 view of the Chernobyl nuclear power plant. Even today, 30 years after, work continues at the site to seal off radiation, with a massive engineering project underway to create a giant concrete sarcophagus for the burned out reactor. The latest project completion date is the end of 2017.

The Chernobyl disaster is an event powerful enough to stoke nuclear fears decades later. But how did it happen? Find out in this timeline.

Founded in 1970, Pripyat -- located about 81 miles from Kiev -- was constructed to be a model for the future Soviet city. Within the town, the Soviet Union built the Chernobyl power plant, which had four 1,000-megawatt reactors.

Pripyat was a modern city for its time, with the facilities and infrastructure to support a population of some 50,000 by 1986, many of whom were workers at the plant. The seemingly idllyic community even had an amusement park.

No one could have expected what happened in the early morning hours of April 26.

Beginning April 25, 1986, workers at the plant began running tests on their facility to determine their emergency preparedness. Against regulations, the plant operators turned off critical emergency safety and cooling systems.

Despite warning of a rise of reactor temperatures, the workers failed to respond appropriately to an increasingly dangerous situation. Pressure began to build.

At 1:23 a.m., a sudden increase in power in reactor four caused a first explosion, which lead to hydrogen leaking into the outside air.

A second chemical explosion followed, literally blowing the top off the plant, releasing a massive amount of highly radioactive debris into the air.

At this point, workers at the plant still did not understand the full magnitude of the disaster. Firefighters arrived some 20 minutes after the explosion, but they had neither the training nor the know-how to deal with this kind of disaster.

Less than an hour after the explosion, at 2:15 a.m., local government officials convened a crisis meeting. They ordered roads blocked, and enlisted the help of thousands of police and firefighters, none of whom are wearing the kind of protective clothing needed for a nuclear crisis.

Plant workers, specifically pump operators tasked with trying to cool the overheated reactor, were the first to respond to the crisis were exposed to fatal doses of radiation. They began to experience symptoms of radiation sickness around 3 a.m. and weakened to the point of barely being able to carry themselves.

Debris from reactor four landed on reactor three, but plant operators didn't shut it down until around 5 a.m. It would be a full 24 hours before reactors one and two were placed offline.

Thanks to the efforts of 37 firefighter brigades, all of the fires at the plant were extinguished by 6:35 a.m. Despite the disaster that occurred overnight, construction crews arrived at 8 a.m. to work on building reactors five and six, apparently unaware of the danger.

That evening, curious residents of Pripyat gathered on a railway bridge to get a view of the power plant. Unfortunately for them, a strong wind blew a lethal dose of radiation over them, and not one survived. The structure was eventually nicknamed the "bridge of death."

Nearly 24 hours after the accident, around midnight on April 27, buses began to arrive to prepare for the evacuation of the residents of Pripyat.

At this point, government officials at the site were under the impression they could still contain it. Helicopters dropped tons of neutrino-absorbing materials, but none reached the core.

Although there was a brief dip in radiation levels, they spiked again around mid-afternoon, and residents had no choice but to evacuate. Because of the immediate threat posed by the disaster, residents were given just a couple of hours to gather their things, and advised only to bring with them the bare essentials.

The official announcement declared that townspeople were leaving their residences "temporarily," which may explain why so many left so much behind. Those that attempted to return, however, were greeted by military or police personnel and quickly learned that Pripyat was lost.

More than 300,000 people in total in an 18-mile radius around Chernobyl were forced out of their homes.

Despite the magnitude of the disaster, the Soviet Union was initially reticent to share the details of what happened with the international community.

On Monday, April 28, Swedish nuclear scientists detected a surge of radioactivity in the atmosphere. Radioactive smoke originating from the Chernobyl site had spread from the western Soviet Union into Europe. Finland and Denmark reported similar findings in their skies as well, raising the pressure for a response.

The Soviet government released a statement acknowledging a nuclear accident, but failed to characterize its scale. In fact, they instead called out the Three-Mile-Island incident in the United States in 1979, as though the Chernobyl disaster had been unfairly overstated, a simple reaction by Western propagandists.

On the morning of April 29, an American satellite captured images of the Chernobyl site and intelligence analysts were stunned to see the extent of the damage at the still-smoking site.

Accurate estimates as a result of the lives lost following the disaster are difficult to come by. Some organizations claim tens of thousands of lives were lost decades later to terminal cancer caused by high levels of radiation exposure. Government studies paint a somewhat less ominous picture.

The effects of severe radiation exposure claimed the lives of 28 of the plant's 600 workers in the first four months following the explosion at reactor four, according to the U.S. Nuclear Regulatory Commission (NRC). A further 106 experienced acute radiation sickness. Cleanup efforts involved more than 600,000 workers, some of whom were exposed to elevated levels of radiation.

Radiation contamination following the accident has affected millions of residents of Ukraine, Russia and Belarus. Milk contaminated with radioactivity led to some 6,000 reported thyroid cancer cases among children since 1986. Ninety-nine percent were successfully treated, the NRC notes. Fifteen of those children affected by thyroid cancer did not survive, however.

Chernobyl today is still potentially a major health hazard, though the site is closely monitored. With people largely long gone from the Chernobyl Exclusion Zone, an area of roughly 1,000 square miles, wildlife has thrived. Populations of deer, elk, boars and wolves took a hit following the disaster. But now they flourish.

Chernobyl also draws another curious sort of creature: tourists. The site is now an offbeat destination for those who find thrills in disaster tourism.

It will be a long time before humans can inhabit the land, up to 320 years in fact. Until then, the ghost town of Pripyat and the husk of the power plant looming in the background will remain a haunting reminder of what was supposed to be a modern marvel.